The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Inorganic binder compositions have been proposed to solidify and dispose harmful wastes. In Davidovits et al. U.S. Pat. Nos. 5,352,427; 5,349,118; 5,342,595; 4,859,367; 4,349,386; 4,472,199; and 4,509,985; in Neuschaeffer et al. U.S. Pat. Nos. 4,522,652; 4,533,393; and 4,608,795; and in Heitzmann et al. U.S. Pat. Nos. 4,640,715 and 4,642,137; a geopolymer comprising alumino-silicate oxide is described. These geopolymers were developed for inclusion in masonry tiles but were found to be useful for solidifying wastes for long term disposal.
Alumino-silicate binders are comprised of two components: a fine dry powder and a syrupy, highly alkaline liquid. The powder is a soluble alkali polysilicate which can be activated by the alkaline liquid to form tetrahedra of SiO4 and AlO4. The tetrahedra are cross-linked by shared oxygen molecules to form inorganic polymeric networks. A mildly exothermic reaction in the alkali activated mixture is accompanied by hardening and polycondensation.
Inorganic binders are characterized by several distinct properties, including thermal stability, high surface smoothness, precise mobility and hard surfaces. As a result, inorganic binders are particularly useful in specialty construction applications, such as saline or aqueous environments.
Further, the inorganic binder compositions of the prior art have been found to provide long term solutions for hazardous and harmful wastes. Various organic and inorganic wastes can be mixed with the inorganic compounds displacing the normal volume of aggregates in forming a monolithic solid. As the crystal structure grows and the solution solidifies, the waste components are co-bound into a lattice, rendering the waste chemically inert, suitable for landfilling, recycling into construction media or reintroduction into a production process. The most significant properties of a waste treated with an inorganic binder is the ability to resist chemical attack from acidic conditions and to transform soft, disaggregated or sludge-like waste into hard, cohesive solids in a relatively short period of time.
Unfortunately, the cost of the raw materials has prevented the inorganic binder compositions of the prior art from being commercially competitive with other existing technologies for long term disposal or recycling of wastes or even with conventional Portland cement.